Analysis of the Standard Enthalpy of Combustion for Alcohols

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Introduction

ï»¿Investigate an Aspect of Organic Chemistry Investigation of the standard enthalpy change of combustion for alcohols Sarah van der Post HL Chemistry IB Internal 24 – 6 - 2012 Design Aim: To investigate the standard enthalpy change of combustion for 5 consecutive alcohols in the alcohol homologous series, methanol, ethanol, propan-1-ol, butan-1-ol and pentan-1-ol, by using a calorimetric method to calculate the heat gained by the 100cm3 water in the experiment, and thus the heat lost by the alcohol lamp at standard temperature and pressure (298 K and 101.3 kPa). Background Knowledge: Alcohols are organic compounds containing Oxygen, Hydrogen and Carbon. The alcohols are a homologous series containing the functional –OH group. As we move down the homologous series of alcohols, the number of Carbon atoms increase. Each alcohol molecule differs by –CH2; a single Carbon atom and two Hydrogen atoms. Combustion is the oxidation of carbon compounds by oxygen in air to form CO2 and H2O. Combustion produces heat as well as carbon dioxide and water. The enthalpy change of combustion is the enthalpy change that occurs when 1 mole of a fuel is burned completely in oxygen. When alcohol undergoes complete combustion it produces carbon dioxide and water as products, and energy is released. The standard enthalpy of combustion of an alcohol (âH°comb) is the enthalpy change when one mole of an alcohol completely reacts with oxygen under standard thermodynamic conditions (temperature of 25°C and pressure of 101.3 kPa). The standard enthalpy change of combustion of alcohols varies depending on their molecular size. The greater the number of carbons, the higher the standard enthalpy of combustion, as there is the presence of more bonds. ...read more.

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